Transponder assembly for use with parallel optics modules in fiber optic communications systems

ABSTRACT

A transponder assembly for use with fiber optic digital communication cables having multiple parallel optic fiber elements. The transponder assembly features a transmitter port and receiver port for connection with separate parallel optic cables for separately transmitting and receiving data and an electrical connector for connecting with computer or communication systems. The transponder assembly includes a parallel optic transmitter module and a parallel optic receiver module having pluggable edge connectors. The assembly also includes a circuit board on which a semiconductor chip useful for signal processing and the electrical connector are mounted. A flex circuit is used in connecting the circuit board to the parallel optic modules. The semiconductor chip and electrical connector are mounted directly across from one another on opposite surfaces of the circuit board.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to the use of optoelectronic components infiber optic digital communication networks and, more particularly, totransponder assemblies which transmit and receive optical signals overfiber optic ribbon cables having multiple fiber optic elements.

2. Discussion of the Background

The majority of computer and communication networks in use today rely oncopper wiring to transmit data between network nodes. However,electrical signals carried by copper wiring have a limited capacity forcarrying digital data.

Many computer and communication networks, including large parts of theInternet, are now being built using fiber optic cabling that can be usedto transmit much greater amounts of data. With fiber optic elements datais transmitted using optical signals (sometimes referred to as photonicsignals) having greater data carrying capacity.

However, since computers use electrical signals as opposed to opticalsignals, the light signals used to transmit data over fiber optic linksmust be translated to electrical signals and vice-versa during theoptical communication process. Building such fiber optic networkstherefore requires optoelectronic modules which electrically andoptically interface optical transmission mediums such as fiber opticcables with electronic computing and communications devices. Further, inorder to provide the required bandwidth for very high-speedcommunications, fiber optic ribbon cables having multiple fiber opticelements and so-called “parallel optics” modules adapted forconcurrently transmitting or receiving multiple signals over such mayalso be used.

The optoelectronic modules associated with fiber optic networks shouldtherefore be adapted for accommodating fiber optic ribbon cables havingmultiple fibers. Further, it is desirable for separate parallel optictransmitter and receiver modules to be incorporated in transponderassemblies which can separately transmit and receive optical data overseparate cables using the transmitter and receiver modules. However, formost applications these transponder assemblies must be compact andshould utilize only the smallest possible footprint on the circuitboards within the electronic computing or communications devices withwhich the fiber optic network is interfacing.

SUMMARY OF THE INVENTION

The transponder assembly of the present invention comprises a small formfactor system for interfacing between computer and communication systemsand fiber optic cables having multiple fiber elements while providingconcurrent electrical-to-optical and optical-to-electrical conversionfunctionality. The transponder assembly features a pair of opticalcommunication ports one of which functions as a transmitter port and theother of which functions as a receiver port for interconnecting withparallel optics fiber optic ribbon cables. The transponder assembly alsofeatures a pin-array electrical connector for interconnecting withcorresponding connectors installed on the circuit boards of theelectrical computer and communications systems being interfaced with.

The transponder assembly includes a parallel optics transmitter moduleand a parallel optics receiver module having pluggable edge connectors.The assembly also includes a circuit board mounting aSerializer/Deserializer (SerDes) chip and the pin-array type electricalconnector. A flexible printed circuit or Flex circuit is used toflexibly connect the circuit board to a connector board mounting a pairof connection jacks which interconnect with the edge connectors of theparallel optics modules. The Flex circuit allows the alignment of thecircuit board and parallel optics modules to be adjusted for providingan assembly having minimum depth dimensions. The SerDes chip andpin-array connector are mounted directly across from one another onopposite surfaces of the circuit board using ball grid arrays havingareas in which their attachments are positioned in between one anotherin the overlapping areas. The solder pads associated with the viashaving the same connection functionality are interconnected by surfacetraces and redundant vias are eliminated in order to allow adequatepathways for circuit traces to within the circuit board structure toextend through the overlapping areas of the ball grid array attachments.Placement of the pin-array connector and the SerDes chip across from oneanother on the circuit board allows for an assembly having minimumlateral dimensions.

It is an object of the present invention to provide a transponderassembly adapted for use with fiber optic ribbon connectors havingmultiple fiber optic elements.

It is another object of the present invention to provide a transponderassembly which utilizes separate parallel optic transmitter and receivermodules in an assembly having a compact size and minimum footprint.

It is a further object of the present invention to provide for theinternal components of a parallel optics transponder assembly to beflexibly interconnected whereby a compact size can be achieved.

It is yet another object of the present invention to provide for asemiconductor chip and an electrical connector to be positioned directlyacross from one another on the same circuit board using ball grid arrayattachments on opposite surfaces of the same circuit board toelectrically interconnect the semiconductor chip, electrical connectorand circuit board.

It is a yet further object to provide an efficient and effectiveparallel optics transponder assembly featuring a compact size and smallfootprint.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention and its advantages may best be understood by reference tothe following description taken in conjunction with the accompanyingdrawings in which:

FIG. 1 is an overhead, perspective view of a transponder assemblyconstructed in accordance with the principles of the present inventionprimarily showing the communication ports by which the assembly can beoptically connected to a pair of fiber optic ribbon cables forseparately transmitting and receiving digital data over separate cables.

FIG. 2 is a perspective view of the underside of the transponderassembly shown in FIG. 1 primarily showing the pin-array connector forelectrically connecting the assembly to a circuit board or the like of acomputer or communications system.

FIG. 3 is an overhead, perspective view of the transponder assembly ofthe present invention with the top section of the assembly housingremoved showing the internal components within the transponder assemblyand showing, among other things, the parallel optic transmitter andreceiver modules within the assembly.

FIG. 4 is a side view of the internal components of the transponderassembly of the present invention showing, among other things, theparallel optic modules, a connector board with connection jacks, a Flexcircuit and a rigid circuit board on which a SerDes chip and pin-arrayconnector are mounted on opposing surfaces of the board.

FIG. 5 is a close-up side view along lines 5—5 in FIG. 4 of theconnector board, Flex circuit and rigid circuit board componentsprimarily illustrating how these components are flexibly interconnectedand aligned.

FIG. 6 is a close-up cross-sectional view of a typical section of therigid circuit board on which the SerDes chip and pin-array connector aremounted showing an area in the vicinity of one of the ball grid arraysassociated with either the chip or the connector.

FIG. 7 is an overhead, plan view of the circuit board on which theSerDes chip and pin array connector are mounted showing the ball gridarray attachment structures associated with the SerDes chip and the pinarray connector.

FIG. 8 is a close-up cross-sectional view of a typical section of therigid circuit board on which the SerDes chip and pin-array connector aremounted showing an area of overlap between both of the ball grid arraysassociated with the SerDes chip and pin-array connector.

FIG. 9 is a close-up overhead, plan view of the circuit board on whichthe SerDes chip and pin array connector are mounted exclusively showingball grid array attachment structures associated with both the SerDeschip and pin-array connector in one of the overlapping areas between theball grid arrays and their attachment structures.

FIG. 10 is an exploded, overhead perspective view of a parallel opticsmodule which comprises one of the primary components of the transponderassembly of the present invention showing, among other things, how thereceptacle, lens and alignment frame, carrier frame section, circuitboard, edge connector and the other components and subcomponents of themodule relate to one another.

FIG. 11 is an enlarged exploded, overhead perspective view of theforward portion of the module shown in FIG. 10 primarily showing, howthe receptacle, lens and alignment frame, carrier frame section andtheir subcomponents relate to one another.

DETAILED DESCRIPTION OF THE INVENTION

The present invention will now be described in detail with reference topreferred embodiments as illustrated in the accompanying drawings. Inthe following description, numerous specific details are set forth inorder to provide a thorough understanding of the present invention.However, it should be apparent to one skilled in the art that thepresent invention may be practiced without some or all of these specificdetails. In other instances it should be appreciated that well-knownprocess steps have not been described in detail in order to not obscurethe present invention.

Referring now to FIGS. 1 and 2, a transponder assembly 10 is shown asincluding a two-piece housing 12, two communication ports 14 and 16, apin-array type electrical connector 18 and a heat sink 20. The pin-arrayconnector 18 is preferably a 300-pin MEG-Array™ electrical connector(which may be purchased from FCI USA, AREVA Group, having US offices at825 Old Trail Road in Etters, Pa., 17319). The two-piece housing 12includes a top section 22 and a bottom section 24 which are fittedtogether to form a small form factor case enclosing the operationalmodules of the transponder assembly 10. The communication ports 14 and16 reside on its front side of the assembly 10 and include paralleloptical link receptacles 26 and 28 which are part of parallel opticsmodules 30 and 32 (not otherwise shown in FIGS. 1 and 2) deployed withinthe transponder 10. The receptacles 26 and 28 are designed to mate withstandard MTP™ (MPO) connectors (Optical Internetworking Forum,OIF-VSR4-03.0) of fiber optic ribbon cables containing 12 parallelfibers and presenting 12 fiber optic terminations for opticalinterconnection. The pin-array connector 18 resides on the underside ofthe transponder assembly 10 and includes a 300-pin plug housing 25 forconnecting to a printed circuit board or other electrical assemblyhaving a matching Pin-array receptacle housing. The port 14 isassociated with the parallel transmitter module 30 which is adapted forconverting electrical signals into optical signals and transmittingthese signals into a fiber optic ribbon cable connector. The port 16 isassociated with the parallel optics receiver module 32 which is adaptedfor receiving optical signals from a fiber optic ribbon cable connectorand converting the same into electrical signals. The ports 14 and 16thereby provide transmitter and receiver links so that the transponder10 can both receive and transmit data over separate 12 fiber elementparallel optic ribbon cables. The heat sink 20 includes a set of ribs 35to allow for improved heat dissipation through the surface of thehousing 12 from the active elements deployed inside the assembly 10.

The transponder 10 is designed to be compliant with O IF (OpticalInternetworking Forum)-VSR4-01.0 implementation standard for opticallytransmitting OC-192data and providing a parallel optics based VSR (VeryShort Reach) OC-192/STM-64 interface. The transponder assembly 10provides a bi-directional interface for multiplexing a sixteen-bit widebus of 622 Mb/s electrical LVDS (Low-Voltage Differential Signal) signaldata supplied from the pin-array connector 18 into twelve channels ofoptical signal data at 1.24 Gb/s for transmission as photonic signalsover a twelve element optical ribbon cable and also for receiving twelvechannels of optical signal data at 1.24 Gb/s and demultiplexing thisdata into a sixteen-bit wide bus of 622 Mb/s electrical LVDS signal datafor supply to the pin-array connector 18. The transponder assembly 10also includes an error detection channel and a protection channel amongthe twelve optical channels. The pin-array connector 18 is intended tointerface to an OC-192 framer on the electrical assembly to which thetransponder assembly 10 is connected.

Referring now to FIG. 3, the transponder assembly 10 includes a paralleloptics transmitter module 30, a parallel optics receiver module 32, aFlexible printed circuit or Flex circuit 34, a rigid circuit board 36and connector board 38 all of which are mounted onto the bottom section24 of the housing 12. The parallel optics transmitter module 30 providesan optical interface to a twelve fiber optic ribbon cable and includes aset of twelve VCSELs (Vertical Cavity Surface Emitting Lasers) foremitting optical signals in response to electrical signals which aredirected into the twelve fibers of the ribbon cable and includeselectrical circuitry for processing electrical signals received from atransmitter edge connector 40 and converting these signals into formssuitable for driving the VCSELs. The parallel optics receiver module 32provides an optical interface to a twelve fiber optic ribbon cable andincludes a set of twelve PIN diodes for responding to optical signalsfrom the twelve fibers of the ribbon cable which are directed onto thediodes and converting these signals into electrical signals and includeselectrical circuitry for processing the electrical signals into suitableforms for general use and supplying them to a receiver edge connector42. The transmitter module 30 includes a frame 44 on which thereceptacle 26, heat sink 46 and a small circuit board 48 are mounted.The circuit board 48 extends along the bottom of the module 30 andcarries the edge connector 40 at its far end opposite the receptacle 26.The receiver module 32 is similarly constructed and includes a frame 45on which the receptacle 28, heat sink 50 and a small circuit board 52are mounted. The circuit board 52 extends along the bottom of the module32 and carries the edge connector 42 at its far end opposite thereceptacle 28. The Flex circuit 34 extends from the circuit board 36 tothe connector board 38 and includes a large number of signal lines whichinterconnect the circuit board 36 to the connector board 38. The Flexcircuit 34 is comprised of a flexible material such as a Polyimidematerial supporting thin metal traces as signal lines that can be curledinto arcuate shapes while still preserving the integrity of its signallines. The rigid circuit board 36 provides electrical circuitry for usein signal processing and includes a SerDes (Serializer/Deserializer)semiconductor chip 54 as well as other circuitry. The connector mountingboard 38 serves as a host for a pair of electrical connection jacks 60and 62 mounted on its underside for pluggably interconnecting with theedge connectors 40 and 42 of the parallel optic modules 30 and 32.

Referring now to FIGS. 4 and 5, the parallel optic modules 30 and 32 areconnected to the connector board 38 by the edge connectors 40 and 42carried on their circuit boards 48 and 52. The edge connectors 40 and 42plug into sockets in the connection jacks 60 and 62 mounted onto theconnector board 38. The connector board 38 and connection jacks 60 and62 are constructed and arranged so that they are reversed with respectto their standard orientation for mounting a parallel optic module on acircuit board. The connector board is flipped over and extends inward tothe center of the assembly 10 and away from its perimeter defined by thehousing 12. A more compact configuration is provided by having theorientation of the connector board 38 reversed so that it does notimpinge on the housing perimeter thereby forcing an increase in housingsize. It should be noted that the module 32, edge connector 42, circuitboard 52 and connection jack 62 are not shown in FIGS. 4 and 5 but arepositioned directly behind the module 30, edge connector 40, circuitboard 48 and connection jack 60. However, discussion of the inventionwith reference to the module 30, edge connector 40, circuit board 48 andconnection jack 60 as illustrated in the drawings should serve to fullyexplain the invention. The connector board 38 is in turn connected tothe circuit board 36 by the Flex circuit 34. However, the Flex circuit34 is curled into a multi-curved shape between the connector board 38and circuit board 36 in order to allow the circuit board 36 to bedeployed at a different level from the connector board 38. The planedefined by the position of circuit board 36 is intermediate between theplanes defined by the positions of the connector board 38 and thecircuit boards 48 and 52. Thus, the planes defined by the circuit board36, the connector board 38, and the circuit boards 48, and 52, are notco-planar. This is of advantage since it allows the top of the circuitboard 38 to define the top of the internal assembly within the housing12 which otherwise would be defined at a higher level by the circuitboard 36 thereby adding to the overall height of the module. Use of theFlex circuit 34 in interconnecting the modules 30 and 32 to the circuitboard allows for a more compact assembly to be achieved which in turnprovides a smaller form factor to the transponder assembly 10.

Referring now again to FIG. 4, the circuit board 36 includes the SerDessemiconductor chip 54 mounted on its top surface 64 and the pin-arrayconnector 18 mounted on its bottom surface 66. The SerDes chip 54 andpin-array connector 18 are mounted directly across from one another onopposing surfaces of the circuit board 36. Both the SerDes chip 54 andthe pin-array connector 18 are connected to the circuit board 36 by ballgrid array attachments 70 and 72 on the opposite surfaces 64 and 66 ofthe circuit board 36.

Referring now to FIG. 6, a small section 75 of the circuit board 36 isshown in the vicinity of one of the ball grid array attachments. Thecircuit board has multiple layers 68 through which circuit traces mayextend at multiple levels. This section 75 of the circuit board 36includes two spaced apart attachment pads 74 on which solder may bedeployed on the surface of the board 36 which are associated with theball grid array. The pads 74 are connected by short circuit traces 76 toa metal plated vias 80 which extend entirely through the board 36 fromsurface to opposite surface. This construction is characteristic of ballgrid arrays and allows the pads 74 to be selectively connected tocircuit traces at any of the layers 68 of the board 36 by way of thetraces 76 and metal plated vias 80.

Referring now to FIG. 7, the attachment pads 74, connection traces 76and vias 80 associated with each of the ball grids array attachments areshown. It should be borne in mind that the circuit board 36 is not shownin this view and that the vias 80 extend through the circuit board 36while the attachment pads 74 and traces 76 for each of the attachments70 and 72 are resident on opposite surfaces of circuit board 36. Theball grid array attachment 70 for the SerDes chip is shown as havingtwo-hundred-fifty-six pads in a square pattern. The ball grid arrayattachment 72 for the pin-array connector 18 is shown as havingthree-hundred pads in a rectangular pattern. The patterns formed by theattachments 70 and 72 define two overlapping areas 84 and 86characterized by high densities of pads and associated traces and vias.Surface traces such as traces 76 may be used to connect to discretesurface mounted components.

Referring now to FIG. 8, a small section 85 of the circuit board 36 isshown in the overlapping area 84. This section 85 of the circuit board36 includes two spaced apart pads 74 a on the surface 64 of the board 36associated with the ball grid array attachment 70. The pads 74 a areconnected by short circuit traces 76 a to a metal plated vias 80 a whichextend entirely through the board 36 from one surface to its oppositesurface. This section 85 of the circuit board 36 also includes twospaced apart pads 74 b (in phantom) on the surface 66 of the board 36associated with the ball grid array attachment 72. The pads 74 b areconnected by short circuit traces 76 b (in phantom) to a metal platedvias 80 b which extend entirely through the board 36 from one surface toits opposite surface. The vias 80 a and 80 b are deployed in analternating pattern so that the vias of one array attachment arepositioned in between the vias of the other array attachment. In thismanner all of the vias 80 for ball grid arrays attachments 70 and 72 canbe accommodated in the available space.

Referring now to FIG. 9, the overlapping area 84 is shown as includingvias 80 associated with each of the ball grid array attachments 70 and72 but only pads 74 a and traces 76 a associated with the attachment 70.The vias 80 c are connected to mutiple pads 74 a in cases where thecircuit functionality allows for such interconnections. Certain vias maythereby be eliminated as redundant which allows for simplerconstruction. More importantly it allows circuit traces at multiplelevels in the circuit board 36 to extend through the via-free pathways,such as space 86, thereby created for establishing connections withinthe board 36.

Referring now to FIGS. 10 and 11, a typical parallel optic (transmitter)module 30 is shown in greater detail as including the receptacle 26,metal support frame 44, lens and alignment frame 92, carrier assembly94, and heat sink 46. It should be noted that the receiver module 32would be similar in design and construction to the transmitter module 30except that it would contain photoactive elements operative forreceiving signals such as PIN diodes and associated circuitry as opposedto transmitter elements such as VCSELs. The receptacle 26 is mounted inthe recess 98 in the support frame 44 so that it abuts the back wall 102of the frame 44. The carrier assembly 94 includes the printed circuitboard 48, the module Flex circuit 106 and the carrier frame section 108.The lens and alignment frame 92 is mounted in between the frame section108 of the carrier assembly 94 and the back wall 102 of the supportframe 44 50 that it is immediately adjacent to the fiber ends on theproximal end of the connector ferrule for the fiber optic ribbon cablewhen the ferrule is latched into the module 30. The Flex circuit 106connects the frame section 108 to the circuit board 48 serving as amedium for providing a large number of connection lines betweencomponents on the carrier frame section 108 and the circuit board 48including the microcontroller chip 110 and the edge connector 40. Thecircuit board 48 fits along the back shelf 112 of the support frame 44underneath the heat sink 46. The front end 114 of the heat sink 46 abutsthe backside of the carrier frame section 108 for dissipating heatgenerated during operation by the electrical components mounted onto theframe section. The bolts 116 help retain the heat sink 46 and circuitboard 48 in position within the frame 44. The support frame 44 includesa window 118 in its back wall 102. The lens and alignment frame 92includes a mostly planar base 120 and a rectangular tower structure 122projecting forward of the base 120 on which guide pins 124 and a lensarray 126 are mounted. The tower structure 122 of the lens and alignmentframe 92 fits through the window 118 of the support frame 44 in theassembled device. The lens and alignment frame 92 is a one-pieceprecision plastic injection-molded part including the tower structure122, guide pins 124 and lens array 126. The carrier frame section 108 ofthe carrier assembly 94 preferably includes one or more layers ofprinted circuit board material including a layer of Flex circuitmaterial which is an extended part of the Flex circuit 106. Anoptoelectronic device 130 containing photoactive semiconductorcomponents is precisely mounted on the frame section 108. The device 130comprises an integrated circuit chip which contains twelve VCSELs whichare deployed on and as part of the chip. The photoactive components aredisposed in a linear array at regular intervals corresponding to thelens array 126 and the array of fibers in the fiber optic ribbon cableconnector. When the lens and alignment frame 92 is mounted on the framesection 108 the optoelectronic device 130 and its photoactive components(VCSELs) are precisely aligned with the lens array 126 and the guidepins 124. One or more signal processing chips 132 may be mounted on thecarrier frame section 108 for communicating with the optoelectronicdevice 130 and more particularly providing drive signals to transmitterelements (or providing signal amplification and conditioning in the caseof receiver elements).

Although only a few embodiments of the present inventions have beendescribed in detail, it should be understood that the present inventionmay be embodied in other forms without departing from the overall spiritor scope of the present invention.

1. An apparatus comprising: a transmitter module having a first edgeconnector, and photoactive transmitting elements, wherein the first edgeconnector is electrically associated with the photoactive transmittingelements, and the first edge connector defines a first plane; a receivermodule having a second edge connector, and photoactive receivingelements, wherein the second edge connector is electrically associatedwith the photoactive receiving elements, and the second edge connectordefines a second plane; a circuit board having a first surface and asecond surface, and wherein the circuit board defines a third plane, andwherein the first plane is not co-planar with the third plane, and thesecond plane is not co-planar with the third plane; a semiconductor chipelectrically connected to the first surface of the circuit board; anelectrical connector electrically connected to the second surface of thecircuit board; a first electrical connection jack electrically connectedto the first edge connector; a second electrical connection jackelectrically connected to the second edge connector; a flex circuitelectrically connected to the circuit board, the first electricalconnection jack, and the second electrical connection jack; and ahousing mechanically securing the transmitter module, the receivermodule, the circuit board, the flex circuit, the first electricalconnection jack, and the second electrical connection jack.
 2. Anapparatus according to claim 1, further comprising a connector board onwhich is mounted the first electrical connection jack, and the secondelectrical connection jack, and wherein the connector board interfaceswith the flex circuit.
 3. An apparatus according to claim 1 wherein theelectrical connector is a pin-array connector, and wherein thesemiconductor chip is a Serializer/Deserializer semiconductor chip. 4.An apparatus according to claim 1 wherein the circuit board includes afirst ball grid array attachment on the first surface of the circuitboard and having a first set of vias for coupling the circuit board tothe electrical connector, and wherein the circuit board includes asecond ball grid array on the second surface of the circuit board andhaving a second set of vias, which overlap the first set of vias, forcoupling the semiconductor chip to the circuit board.